1. Field of the Invention
This invention relates to a vehicle behavior detection apparatus for detecting a state of unstable behavior such as understeer, etc., of a vehicle during traveling (hereinafter simply referred as an “unstable state”).
2. Description of the Related Art
Conventionally, there has been proposed a vehicle state detection apparatus as a vehicle behavior detection apparatus that detects an unstable state (an understeer state, etc.) of a vehicle during the time when the vehicle is traveling (see, for example, a first patent document: Japanese patent application laid-open No. 2003-341538).
A vehicle state detection apparatus described in the first patent document includes a standard alignment torque calculating unit that calculates a standard alignment torque corresponding to a standard road surface reaction torque, an alignment torque measuring unit that detects an actual alignment torque corresponding to a road surface reaction torque which a vehicle traveling on a road receives from the surface of the road, an alignment torque deviation calculating unit that calculates an absolute value of a deviation between the actual alignment torque and the standard alignment torque as an alignment torque deviation, and a vehicle behavior stability determining unit that compares the alignment torque deviation with a predetermined amount, and determines that the behavior of the vehicle is unstable when the alignment torque deviation is equal to or larger than the predetermined amount, wherein an unstable state of the vehicle during traveling is determined by using the absolute value of the deviation between the standard alignment torque and the actual alignment torque.
In addition, the vehicle state detection apparatus described in the aforementioned first patent document further includes a torque/steering angle calculating unit that calculates the rates of change of the actual alignment torque and the steering angle from the time rate of change of the actual steering wheel operation angle and the time rate of change of the actual alignment torque, wherein the unstable state of the vehicle during traveling is determined by using the rates of change of the actual alignment torque and the steering angle.
In the conventional vehicle behavior detection apparatus, the absolute value of the deviation between the standard alignment torque and the actual alignment torque or the rates of change of the actual alignment torque and the standard alignment torque is used to determine the unstable state of the vehicle during traveling, but no consideration has been given to bad travel environments in which the vehicle is traveling on a bad road such as a cant road (i.e., a sloped surface road), a unpaved road, or the like, so there has been a problem that an incorrect determination on the unstable state of the vehicle might be made depending upon the travel environment of the vehicle.